1. Field of the Invention
The present invention relates to a medium feeding device.
2. Description of the Related Art
Conventionally, a medium feeding device is known that supplies one medium as a transportation target one by one from among a plurality of stacked media. The medium feeding device can separate the medium of one sheet as a transportation target from other media and sequentially convey it, by introducing the medium between a feeding roller, which conveys the medium in a conveying direction, and a brake roller, which generates rotational load in a direction counter to the conveying direction.
In such a medium feeding device, it is desirable to avoid a paper feed failure and a double feed even when a variety of media which differ in friction characteristics or strength are used. For example, Japanese Patent No. 3660547 discloses a technology which appropriately changes a rotational load of a brake roller by controlling an electromagnetic brake. In this way, suitable rotational load can be set for each of a variety of media. This contributes to avoidance of fault, such as a double feed.
Incidentally, there is the demand for improvement in medium conveying speed of a medium feeding device to increase business efficiency or cost performance. In order to secure sufficient performance of separating a medium as a transportation target from the other media when the medium feeding device operates at a high medium conveying speed, it is necessary for a brake roller to generate a rotational load as promptly as possible when a paper feed failure or double feed occurs.
However, in the conventional technologies disclosed in Japanese Patent No. 3660547, in general an element with large inertia, such as an electromagnetic brake, is used to change the rotational load. For this reason, when the medium conveying speed is made higher, a response at the time of the brake roller generating the rotational load is deteriorated due to the influence of the inertia of the element that changes the rotational load. Therefore, in such a case, there is a risk that a medium as a transportation target cannot be reliably separated from the other media.